Reef

Lore & Background

The word 'reef' traces its origins back to the Old Norse word rif, meaning 'rib' or 'reef', which comes from the Proto-Germanic term ribją meaning 'rib'. Reefs may be classified in terms of their origin, geographical location, depth, and topography. Biotic reef types include oyster reefs and sponge reefs, but the most massive and widely distributed are tropical coral reefs. Although corals are major contributors to the framework, the organisms most responsible for reef growth against ocean waves are calcareous algae, especially coralline algae.

Oyster larvae prefer to settle on adult oysters, developing layers that build upward into a massive calcium carbonate structure on which other reef organisms like sponges and seaweeds can grow. Biotic reef types take additional names depending on how the reef lies in relation to land: fringing reefs are attached to a landmass, barrier reefs form a calcareous barrier around a landmass resulting in a lagoon, and atolls are ring reefs with no land present. The reef front, facing the ocean, is a high energy locale, while the internal lagoon is at lower energy with fine grained sediments.

Reader's Guide

Reefs are significant as both natural and artificial structures that provide shelter to various aquatic animals, helping prevent extinction. Artificial reefs are sometimes designed to increase the physical complexity of featureless sand bottoms to attract a more diverse range of organisms, and fish farmers sometimes invest in them for aquaculture. Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information and may serve as traps or conduits for fossil fuels or mineralizing fluids to form petroleum or ore deposits. Corals, including extinct groups Rugosa and Tabulata, have been important reef builders through much of the Phanerozoic since the Ordovician Period.

Other organism groups, such as calcifying algae, molluscs (especially rudist bivalves during the Cretaceous Period), and Archaeocyatha during the Cambrian Period, have created massive structures. The corals that build reefs today, the Scleractinia, arose after the Permian–Triassic extinction event and became increasingly important reef builders throughout the Mesozoic Era. Artificial reefs, built by sinking oil rigs, scuttling ships, or deploying rubble, provide stable hard surfaces where algae and invertebrates attach, in turn providing intricate structure and food for assemblages of fish.

Did You Know?

• Earth's largest coral reef system is the Great Barrier Reef in Australia, at a length of over 2300 km.
• Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms but still exist today.